Guided Wave Beamforming Imaging Using Polar Coordinate Laser Scanning

In this paper, we propose a technique for efficiently detecting damage in plate-like structures using guided waves, polar coordinate-based beamforming imaging, and filtering techniques. The proposed technique uses a laser Doppler vibrometer and a scanning mirror-tilting device for ultrasonic wave imaging, with single-frequency excitation provided by a mounted piezoelectric transducer. Frequency-wavenumber domain filtering and directional filtering are implemented in polar coordinates for efficient detection of damage-reflected waves by removing any incident wave components. The filtered waves are then processed using a delay-and-sum beamforming algorithm within local-area laser scanning through a circular array sensing system. The polar coordinate-based laser scanning system improves the damage detection capability and processing time by removing the need for coordinate transformation in frequency-wavenumber domain filtering and directional filtering. Finally, the proposed technique is validated through experiments on composite and aluminum plates with various types of damage, where it demonstrates improved accuracy and speed when estimating the exact damage location.